1. Field of the Invention
The present invention relates to a light emitting element array and an image forming apparatus utilizing that array.
2. Description of the Related Art
As an exposure light source embodying a light emitting element array in which several thousands of light emitting diodes and the like are arranged in a predetermined manner has been used for an electrophotographic printer. For example, element structures each formed of several AlGaAs layers are provided on a compound semiconductor substrate made of GaAs, and an array configuration is formed from the element structures (see Japanese Patent No. 3185049).
When a light emitting element array is used for printers, it is necessary to determine an element size and a distance between elements in accordance with a desired degree of print resolution. When the resolution is represented by 600 dots per inch, the element size must be 40 μm square or less, and the distance between elements must be about 40 μm. In addition, when the resolution is represented by 1,200 dots per inch, the element size and the distance between elements are necessarily decreased to half or less of the above respective values. These elemental sizes are smaller by approximately two orders of magnitude in terms of area than the size (approximately 200 μm square or more) of a general light emitting diode. Furthermore, these small elements are required to be separately operated.
In order to form an array having small light emitting elements which can be separately driven as described above, it is necessary to electrically isolate elements adjacent to each other, and as methods therefor, for example, the following two may be mentioned. As a first method, a pn junction structure is uniformly formed during epitaxial growth, followed by element isolation by etching (Japanese Patent No. 3426834); and as a second method, element isolation is performed by selective diffusion of Zn which is a p-type impurity (Japanese Patent No. 3236463).